Mass core



Patented Nov. 24. 1931 "UNITED STATES PATENT OFFICE nawru xmmtna, or BERLIN, GERMANY, A SSIGNOR TO THE main or namsrorr- METALL axrmuensnnnscnarr (HAMETAG), or 1aunnm-comrmcx, GERMANY mass'coan No Drawing. Application filed April 14, 1330; Serial No. 444,349, and in Gerniany April 18, 1929.

This invention relates to a so-called mass core, that is to say, to a core made of magnetizable metal powder which is compressed so as to form a practically solid-mass or core, and which is intended for use in induction coils, Pupin coils, and the like. The suitability of a core of this kind tor the purpose forwhich it is intended depends in a great measure upon the insulation of thc'individual particles of the pulverulent metalwith respect to one another. Obtaining the proper insulation is in many cases very difficult, especially 1f the partlcles are not of actually globular shape. This is true, therefore, especially if the particles are in lamelliferous state.

Furthermore, the difficulties grow c0nsiderably if only small amounts of the insulating means are to be used.

It has already been tried to manufacture cores of the kind stated with the aid bf a variety of insulating materials, but the internal phenomena coming into play when the pulverulent metal is compressed together with the respective insulating substance have not been sufliciently considered so that the results have been unsatisfactory.

The present invention starts fromthe idea to produce insulating layers that take in account in a great measure the phenomena occurring during the pressing procedure,'-so that with the aid of these layers also such' metal powders, the parti les of which can be insulated only with diflicult'y, can be transformed or converted into .well insulated cores.

Another advantage which this improved method and core presents resides therein that in such cases in which lacs or lac-like substances, such as shellac, bakelite or the like,- are used great savings can be had.

Concerning the phenomena going on in the core duringthepressing procedure the following points must be paid attention to:

Even if the specific surface pressure is kept in moderate limits during the pressing, still. very considerable pressure can arise, and arises, between the individual particles of the pulverulent'material, as they touch one another only in an imperfect manner, and owing to this great pressure the insulating layers which consists, for instance, of resin are crushed and pressed away at a more or less great number of places. The same detri= mental result is experienced it other hard and solid insulating materials, as for instance cement. glass, mica and the like, are employed.

It, on the other hand, the pulverulent material, i. e. the metal powder, or the ressing mold is heated and kept hot during t 1e pressing operation, as has been proposed by prior inventors in order to render the insulating layers supple orpliable, then the risk arises that the insulation is, at certain individual places or spots, melted and flows away, or is again pressed away, as already stated in the preceding paragraph.

If higher pressures are made use of there arise in the pressed body, as in shaped metal pieces that are subjected to pressure in red heat, so-called flow-lines, that is to say, there arise displacements or dislocations in certain definite directions, especially vertically with respect to the direction inwhich the material is subjected to pressure, the individual particles of the respective material being,

thus, shifted relatively to one another. The

result, thus, is that a certain flow of the ma- .terial towards the wall of the mold takes place pressures. and vs 'hicln besides, does not melt when being heated. Therespective material has also a very considerable tensile stre s,

may be only in one direction or in several directions, but nevertheless it subtle or pliable enough to accommodate itself to the irregularities of the metal particles. and at the same time it is able to withstand the strain to which it is exposed by the pressing procedure.

There are employed for the purpose in view fibrous and yielding substances, such as silk, cotton and paper, especially silk paper. .The respective substance is used in the state of a very fine or minute disintegration, and it is suited to the purpose to disintegrate the respective material in such a degree that these particles when looked at through a microscope appear transparent. At any rate, they are considerably thinner than the metal particles to be insulated, and their length does not exceed the circumference of the same.

The finer the fibrous particles are chosen, the better is their insulating effect, and corresponding to their fineness they may even be shorter than above stated.

The pulverulent metal is intimately mixed with the disintegrated insulating material, and an agglutinant, for instance one of the known lacs, such as bakelite, shellac or the like, is admixed, the mass being then molded and pressed so as to form the desired cores. There are, thus, used, two kinds of insulating substances which co-act in a very useful manner. The lac protects the solid fibrous insulating substance from hygroscopic influences and binds it to the individual metallic particles so that detrimental displacements or dislocations thereof during the pressing operation are prevented, and on the other hand the fine fibrous particles which form, as it were, a net-work upon the metallioparticles prevent the lac from being completely squeezed ofl these particles. Cores manufactured in this manner possess an excellent insulation also at their boundary surfaces, and this very useful efi'eet exists also if the metallic particles have laminiferous shape,

" these particles showing especially the phenomenon of flowing during the pressing, as has already been stated.

In contradistinetion to mass cores made with the aid of merely an insulating lac, as mentioned in the introductory part of this specification, my improved cores present, hesides their technical advantages, also the commercial advantages that about two thirds or even more of the lac can be saved in that the by far cheaper silk paper or the like is sub- .ttituted therefor. If the metal particles are practically globular, a mixture of one part of lac or shellac etc. andof two parts ofvery finely disintegrated silk-paper is used. With from 2% to 3% by weight of the insulating mixture and with the application of a pres sure of from 12000 to 14000 kg. per cm. iron cores can be produced which answer all technical requirements at the utmost degree.

The invention can be carried out practically, for instance, in this way, that first the fibrous material and the insulating lac are intimately mixed with one another whereafter also the pulverulent metal is added and another intimate mixing takes place. Then present prescribed to the mass is left to itself so as to dry and become ri 'd, then it is disintegrated merely by rubbing, then the particles are filled into the respective mold in which the mass is now subjected to the high pressure stated whereby it is transformed into the desired cores.

Another manner of proceeding is this to mix first the fibrous particles and the metal particles, and to add only now the lac, but not the whole amount thereof at .a time but intermittently, or in stages respectively, whereby a more thorough and uniform mixture and mass is attained. A particularly useful mode of carrying out this procedure .is this, first to add a certain small amount of the lac to the mixture of the fibrous particles and the metal particles; then that entire mixture is permitted to dry and grow solid, then the mass is disintegrated by rubbing or the like and the next amount or part-amount of the lac is added, this new mixture is again left to itself so as to become dry and solid, and, if desired, this procedure may be repeated, although in general two stages will do; but, if preferred, more than two may be employed.

I claim:

1. A mass core of compressed magnetizable pulverulent metal, in which the metal particles are insulated from one another by a very finely disintegrated fibrous substance, the degree of disintegration being such that the fibrous particles are considerably thinner than the said metal particles, and are not longer than the circumference of the same.

2. A mass core of highly compressed magnet-izable metal particles, in which these particles are insulated from one another by a mixture of a lac and a disintegrated fibrous material, the degree of disintegration being such that the particles of said material are considerably thinner than the metal particles netizable metal particles, in which these particles are insulated from one another by a mixture of an agglutinant and a disintegrated fibrous material, the degree of disentegration being such that the particles of said material are considerably thinner than the said metal particles and are no longer than the circumference of the same.

In testimony whereof I affix mv signature.

- ERWIN KRAMER. 

